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Static and Dynamic Disorder of Charge Transfer States Probed by Optical Spectroscopy
Author(s) -
Kahle FrankJulian,
Rudnick Alexander,
Wedler Stefan,
Saxena Rishabh,
Ammenhäuser Robin,
Scherf Ullrich,
Bagnich Sergey,
Bässler Heinz,
Köhler Anna
Publication year - 2022
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.202103063
Subject(s) - materials science , photoluminescence , singlet state , acceptor , excited state , spectroscopy , absorption (acoustics) , chemical physics , absorption spectroscopy , emission spectrum , molecular physics , atomic physics , spectral line , optoelectronics , condensed matter physics , physics , optics , quantum mechanics , composite material , astronomy
Since the key role of charge transfers (CT) states has been identified for organic solar cells (OSCs), research into their properties is a timely topic. Conventionally, their absorption and emission spectra are described in terms of Marcus’ electron transfer theory. This is a single site approach with the essential parameter being the reorganization energy. Thus, it ignores ensemble effects, notably the role of static disorder that is inevitably present in a spin‐coated OSC film. Here time dependent photoluminescence spectroscopy is applied on blends of the polymeric donor MeLPPP with either the non‐fullerene acceptor SF‐PDI 2 or with PC 61 BM within a temperature range from 295 to 5 K. The authors monitor how initially excited singlet states are converted to emissive CT states. Concomitantly, emission from residual singlets on the acceptor is observed rather than hybrid CT‐states. The role of spectral diffusion in this process is discussed. From the temperature and time dependent linewidths of absorption, fluorescence, and CT emission, the static and dynamic contributions to the total disorder are inferred. In both blends, at 295 K, the contribution of static disorder is comparable to the dynamic disorder.